Whether you're playing by ear or by sight, having the current scale baked into muscle memory makes it a lot easier to hit the right next note on the first attem

Whether you're playing by ear or by sight, having the current scale baked into muscle memory makes it a lot easier to hit the right next note on the first attempt. Otherwise you'll be frequently off by a semitone, or end up using non-optimal finger positions (which can be hard to unlearn). Any given melody will modulate between multiple major and minor scales; see Coltrane's "Giant Steps" for an extreme example.